[AMDGPU][GlobalISel] Avoid selecting S_PACK with constants

If constants are hidden behind G_ANYEXT we can treat them same way as G_SEXT.
For that purpose we extend getConstantVRegValWithLookThrough with option
to handle G_ANYEXT same way as G_SEXT.

Differential Revision: https://reviews.llvm.org/D92219

Author: mbrkusanin

llvm/include/llvm/CodeGen/GlobalISel/Utils.h

@@ -146,10 +146,13 @@ struct ValueAndVReg {
 /// When \p LookThroughInstrs == false this function behaves like
 /// getConstantVRegVal.
 /// When \p HandleFConstants == false the function bails on G_FCONSTANTs.
+/// When \p LookThroughAnyExt == true the function treats G_ANYEXT same as
+/// G_SEXT.
 Optional<ValueAndVReg>
 getConstantVRegValWithLookThrough(Register VReg, const MachineRegisterInfo &MRI,
                                   bool LookThroughInstrs = true,
-                                  bool HandleFConstants = true);
+                                  bool HandleFConstants = true,
+                                  bool LookThroughAnyExt = false);
 const ConstantFP* getConstantFPVRegVal(Register VReg,
                                        const MachineRegisterInfo &MRI);
 

llvm/lib/CodeGen/GlobalISel/Utils.cpp

@@ -283,7 +283,7 @@ Optional<int64_t> llvm::getConstantVRegSExtVal(Register VReg,
 
 Optional<ValueAndVReg> llvm::getConstantVRegValWithLookThrough(
     Register VReg, const MachineRegisterInfo &MRI, bool LookThroughInstrs,
-    bool HandleFConstant) {
+    bool HandleFConstant, bool LookThroughAnyExt) {
   SmallVector<std::pair<unsigned, unsigned>, 4> SeenOpcodes;
   MachineInstr *MI;
   auto IsConstantOpcode = [HandleFConstant](unsigned Opcode) {
@@ -310,6 +310,10 @@ Optional<ValueAndVReg> llvm::getConstantVRegValWithLookThrough(
   while ((MI = MRI.getVRegDef(VReg)) && !IsConstantOpcode(MI->getOpcode()) &&
          LookThroughInstrs) {
     switch (MI->getOpcode()) {
+    case TargetOpcode::G_ANYEXT:
+      if (!LookThroughAnyExt)
+        return None;
+      LLVM_FALLTHROUGH;
     case TargetOpcode::G_TRUNC:
     case TargetOpcode::G_SEXT:
     case TargetOpcode::G_ZEXT:
@@ -343,6 +347,7 @@ Optional<ValueAndVReg> llvm::getConstantVRegValWithLookThrough(
     case TargetOpcode::G_TRUNC:
       Val = Val.trunc(OpcodeAndSize.second);
       break;
+    case TargetOpcode::G_ANYEXT:
     case TargetOpcode::G_SEXT:
       Val = Val.sext(OpcodeAndSize.second);
       break;

llvm/lib/Target/AMDGPU/AMDGPUInstructionSelector.cpp

@@ -597,9 +597,11 @@ bool AMDGPUInstructionSelector::selectG_BUILD_VECTOR_TRUNC(
   const DebugLoc &DL = MI.getDebugLoc();
   MachineBasicBlock *BB = MI.getParent();
 
-  auto ConstSrc1 = getConstantVRegValWithLookThrough(Src1, *MRI, true, true);
+  auto ConstSrc1 =
+      getConstantVRegValWithLookThrough(Src1, *MRI, true, true, true);
   if (ConstSrc1) {
-    auto ConstSrc0 = getConstantVRegValWithLookThrough(Src0, *MRI, true, true);
+    auto ConstSrc0 =
+        getConstantVRegValWithLookThrough(Src0, *MRI, true, true, true);
     if (ConstSrc0) {
       const int64_t K0 = ConstSrc0->Value.getSExtValue();
       const int64_t K1 = ConstSrc1->Value.getSExtValue();

llvm/test/CodeGen/AMDGPU/GlobalISel/inst-select-build-vector-trunc.v2s16.mir

@@ -579,10 +579,8 @@ body: |
   bb.0:
 
     ; GFX9-LABEL: name: test_build_vector_trunc_s_v2s16_anyext_constant_anyext_constant
-    ; GFX9: [[S_MOV_B32_:%[0-9]+]]:sreg_32 = S_MOV_B32 123
-    ; GFX9: [[S_MOV_B32_1:%[0-9]+]]:sreg_32 = S_MOV_B32 456
-    ; GFX9: [[S_PACK_LL_B32_B16_:%[0-9]+]]:sreg_32 = S_PACK_LL_B32_B16 [[S_MOV_B32_]], [[S_MOV_B32_1]]
-    ; GFX9: S_ENDPGM 0, implicit [[S_PACK_LL_B32_B16_]]
+    ; GFX9: [[S_MOV_B32_:%[0-9]+]]:sreg_32 = S_MOV_B32 29884539
+    ; GFX9: S_ENDPGM 0, implicit [[S_MOV_B32_]]
     %0:sgpr(s16) = G_CONSTANT i16 123
     %1:sgpr(s16) = G_CONSTANT i16 456
     %2:sgpr(s32) = G_ANYEXT %0

llvm/test/CodeGen/AMDGPU/GlobalISel/llvm.amdgcn.fdot2.ll

@@ -116,18 +116,14 @@ define float @v_fdot2_inline_literal_a(<2 x half> %b, float %c) {
 ; GFX906-LABEL: v_fdot2_inline_literal_a:
 ; GFX906:       ; %bb.0:
 ; GFX906-NEXT:    s_waitcnt vmcnt(0) expcnt(0) lgkmcnt(0)
-; GFX906-NEXT:    s_movk_i32 s4, 0x4000
-; GFX906-NEXT:    s_pack_ll_b32_b16 s4, s4, s4
-; GFX906-NEXT:    v_dot2_f32_f16 v0, s4, v0, v1
+; GFX906-NEXT:    v_dot2_f32_f16 v0, 2.0, v0, v1 op_sel_hi:[0,1,1]
 ; GFX906-NEXT:    s_setpc_b64 s[30:31]
 ;
 ; GFX10-LABEL: v_fdot2_inline_literal_a:
 ; GFX10:       ; %bb.0:
 ; GFX10-NEXT:    s_waitcnt vmcnt(0) expcnt(0) lgkmcnt(0)
 ; GFX10-NEXT:    s_waitcnt_vscnt null, 0x0
-; GFX10-NEXT:    s_movk_i32 s4, 0x4000
-; GFX10-NEXT:    s_pack_ll_b32_b16 s4, s4, s4
-; GFX10-NEXT:    v_dot2_f32_f16 v0, s4, v0, v1
+; GFX10-NEXT:    v_dot2_f32_f16 v0, 2.0, v0, v1 op_sel_hi:[0,1,1]
 ; GFX10-NEXT:    s_setpc_b64 s[30:31]
   %ret = tail call float @llvm.amdgcn.fdot2(<2 x half> <half 2.0, half 2.0>, <2 x half> %b, float %c, i1 false)
   ret float %ret
@@ -137,18 +133,14 @@ define float @v_fdot2_inline_literal_b(<2 x half> %a, float %c) {
 ; GFX906-LABEL: v_fdot2_inline_literal_b:
 ; GFX906:       ; %bb.0:
 ; GFX906-NEXT:    s_waitcnt vmcnt(0) expcnt(0) lgkmcnt(0)
-; GFX906-NEXT:    s_movk_i32 s4, 0x4000
-; GFX906-NEXT:    s_pack_ll_b32_b16 s4, s4, s4
-; GFX906-NEXT:    v_dot2_f32_f16 v0, v0, s4, v1
+; GFX906-NEXT:    v_dot2_f32_f16 v0, v0, 2.0, v1 op_sel_hi:[1,0,1]
 ; GFX906-NEXT:    s_setpc_b64 s[30:31]
 ;
 ; GFX10-LABEL: v_fdot2_inline_literal_b:
 ; GFX10:       ; %bb.0:
 ; GFX10-NEXT:    s_waitcnt vmcnt(0) expcnt(0) lgkmcnt(0)
 ; GFX10-NEXT:    s_waitcnt_vscnt null, 0x0
-; GFX10-NEXT:    s_movk_i32 s4, 0x4000
-; GFX10-NEXT:    s_pack_ll_b32_b16 s4, s4, s4
-; GFX10-NEXT:    v_dot2_f32_f16 v0, v0, s4, v1
+; GFX10-NEXT:    v_dot2_f32_f16 v0, v0, 2.0, v1 op_sel_hi:[1,0,1]
 ; GFX10-NEXT:    s_setpc_b64 s[30:31]
   %ret = tail call float @llvm.amdgcn.fdot2(<2 x half> %a, <2 x half> <half 2.0, half 2.0>, float %c, i1 false)
   ret float %ret